1. Field of the Invention
The present invention relates generally to a document read apparatus for optically reading an image recorded on a document, in particular, to a document read apparatus and an image forming apparatus for reducing a degradation of quality of image read from a document, even when the document is in the form of a book.
2. Description of Related Art
A document read apparatus, such as a scanner or a copy machine, is widely used for optically reading an image recorded on a document and for generating image data. FIG. 15 is a schematic cross-sectional view showing a configuration of a conventional document read apparatus. The conventional document read apparatus includes: a transparent scanner platen 98 to place a document on; light source unit 90 having a light source 91, reflector 92 and a first mirror 93; second mirror 94, third mirror 95, lens 96 and an image sensor 97. The light source 91 is a linear light source that consists of a halogen lamp, xenon lamp or the like. FIG. 15 shows a cross-section that is perpendicular to a line of the light source 91. The image sensor 97 consists of a linear optical sensor, such as a charge coupled device (CCD) and a complementary metal oxide semiconductor (CMOS). A direction along the line of the light source 91 is referred to as a main scanning direction, while a direction perpendicular to the line of the light source 91 is referred to as a sub scanning direction. In FIG. 15, the main scanning direction is perpendicular to the plane direction of the figure, while the sub scanning direction is parallel to the longitudinal direction of the figure.
Light emitted from the light source 91 and light reflected from the reflector 92 are supplied to a document on the scanner platen 98. Light reflected by the document is reflected by the first mirror 93, second mirror 94 and the third mirror 95. The light is then focused by the lens 96 and received by the image sensor 97. In FIG. 15, light paths are represented by arrows. The image sensor 97 outputs image data representing one line image obtained by reading the document, in accordance with a received light quantity. The light source unit 90 moves in the sub scanning direction, while the second mirror 94 and the third mirror 95 moves in synchronization with the light source unit 90 and moves at half the speed of the light source unit 90 in the sub scanning direction. Thus, the document is sequentially read on a line-by-line basis. An image data on a page-by-page basis is generated by performing image processing on the image data outputted by the image sensor 97. If the conventional document read apparatus is a copy machine, an image recording process is performed in accordance with the image data. If the conventional document read apparatus is a scanner, the image data is sent to an external device. Japanese Patent Application Laid-Open No. 2002-314760 discloses an image read apparatus whose light source consists of plural point light sources, such as light emitting diodes (LEDs), arranged parallel to the main scanning direction.